1. Field of the Invention
This invention relates to vehicle safety apparatus, and more particularly to a steering wheel mounted air bag safety system that is connected with apparatus mounted in another relatively stationary part of the vehicle.
2. Description of the Prior Art
The gas generator or inflator of an air bag safety system for protecting the driver of a vehicle is advantageously mounted on the steering wheel. A major problem with steering wheel mounted inflator systems is the interface to the inflator to ignite it. Such a mounting requires that the connection for igniting the inflator must include a connector or coupling assembly which provides for relative motion between the steering wheel and the steering column while maintaining an ignitive connection between the inflator and a collision responsive sensor that usually is located in another and remote part of the vehicle. Space in the steering column is limited and the steering wheel is turned a great many times during the operation of the vehicle. The coupling assembly at the interface must, therefore, be both compact and reliable in operation. It must assure reliable operation during the life of the vehicle in which it is installed, which may be ten (10) years or longer.
For providing such coupling at the interface a steering wheel mounted inflator, electrical coupling arrangements have been proposed in the prior act as disclosed in U.S. Pat. No. 3,525,536, issued to J. C. Pruneski on Aug. 25, 1970 and in U.S. Pat. No. 3,876,272 issued to M. Tsutsumi et al. on Apr. 8, 1975.
In U.S. Pat. No. 3,525,536 the coupling comprises a flexible printed circuit strip that is loosely coiled around the steering shaft with one end thereof electrically connected to the shaft. The other end of the strip is electrically connected to the steering column. Slack in the strip is taken up or decreased by rotation of the steering wheel in one direction and re-established or increased by rotation of the steering wheel in the opposite direction.
The coupling assembly provided in U.S. Pat. No. 3,876,222 comprises a bearing having an inner race and an outer race with an electrically conductive lubricant hermetically sealed therein. The inner race and the outer race are secured to the steering shaft and steering column, respectively, each through an individually associated insulator. A first electrical cord leading to the inflator and a second electrical cord leading to a power source are connected to the inner race and outer race, respectively.
It also known in the art to provide an electrical coupling assembly including slip rings and contact buttons or brushes to the inflator. Such an arrangement is disclosed in U.S. Pat. No. 4,218,073 issued to W. D. Cymbal on Aug. 19, 1980.
The use of electrical circuity is disadvantageous in a number of respects when employed in vehicle safety apparatus. This is for the reason that it may cause false or unwanted operation due to extraneous electrical currents or electromagnetic radiation, or operation, when required, may not occur due to failure of the electrical power source or shorting out of the circuitry. Electrical circuits also tend to become unreliable in operation over long periods of time as a result of wires becoming brittle and breaking. With circuits involving slip rings and brushes, there is difficulty, also, in maintaining circuit continuity, particularly in cold and freezing weather during which ice film formations or contact corrosion tend to break circuit continuity.
As an alternative to the actuation of a steering wheel mounted inflator by electrical circuity, it is known in the art to use pyrotechnic means for activating the inflator. Pyrotechnic inflator activating systems have certain advantages over electrical systems. These advantages include the following:
(a) they operate independently of electrical power; PA1 (b) they can't be fired inadvertently by electrical disturbance or electromagnetic radiation; PA1 (c) they provide long-term reliability; PA1 (d) they require little maintenance; PA1 (e) they are insensitive to freezing weather; and PA1 (f) they are relatively safe to manufacture.
As with electrical systems, problems have been experienced with pyrotechnic inflator activating systems in respect of difficulty encountered in coupling the ignitive reaction or shock wave between a relatively stationary portion of the system, a collision responsive sensor, and a relatively movable portion, specifically, the inflator mounted on the steering wheel.
A pyrotechnic system, at disclosed in U.S. Pat. No. 3,552,796 issued to R. M. Kemmerer et al. on Jan. 5, 1971, utilizes a mechanical sensor which fires a percussion primer upon the occurrence of a collision and a detonating fuse assembly for transmitting the percussive shock wave to a steering wheel mounted inflator. In order to enable the inflator to be rotated with the steering wheel relatively to the steering column, a coupling assembly is provided comprising a loop or ring of detonating fuse which is mounted on the steering wheel and extends from the inflator to an area of the steering wheel immediately adjacent to and concentric with the steering column. Mounted on the steering column, spaced from but in close proximity to the loop of detonating fuse, are a pair of spaced apart blasting caps that are connected by the detonating fuse assembly to the percussion primer in the sensor. Upon rotation of the steering wheel, the loop of detonating fuse is rotated so that part of it is at all times immediately adjacent to both of the blasting caps.
Another assembly for coupling a percussive shock wave from a remotely located sensor to a relatively movable inflator mounted on the steering wheel of a vehicle is disclosed in U.S. Pat. No. 4,272,102 issued to F. B. Burkdoll June 9, 1981. That arrangement includes first and second relatively movable but rigid body members with an annular transmission channel for ignitive reactions in one of the body members. The transmission channel comprises a groove that is coated with exothermal material. Pyrotechnic transmission lines are connected to the body members from the sensor and the inflator for communication through the transmission channel, this notwithstanding relative movement of the body members.
Such pyrotechnic coupling arrangements of the prior art are rather complex, involving many component parts. In addition, they require special sealing provisions for containing the ignition reaction and do not lend themselves readily for use in existing steering columns of vehicles without major rework. Thus, there is a need and a demand for further improvement in the art for solving the interface problem to the steering wheel mounted inflator to ignite it.